The Organic Mechatronics and Smart Materials Laboratory has previously reported a photosensitive electroactive polypyrrole (PPy) composite resin. The photosensitivity of this resin overcame common issues associated with conjugated polymer device fabrication such that complex 3D structures can now be fabricated via light-based additive manufacturing methods. While this resin formulation enabled the fabrication of previously achievable structures and devices, it also required the introduction of copolymers bisphenol A ethoxylate dimethacrylate and polyethylene glycolmethyl ether methacrylate (BEMA-PEGMA). These copolymers improved the mechanical stability of 3D structures with a concomitant trade-off with the electroactive properties of the composite. This study investigates the introduction of PPy coated carbon nanotubes (CNTs) to improve the electrical and electrochemical properties of the composite material. The effect on performance of the composite was investigated by creating stable dispersions of PPy-CNTs at loading factors from 1 9 mg/mL directly into the pyrrole monomer. The electrical conductivity, electroactive response, and suitability for 3D fabrication of the composite has been assessed. 3D transducers fabricated using this new formulation are shown to exhibit feature resolution comparable to the original resin formulation. Finally, the improved electrical conductivity of the material is assessed to enable the post-hoc deposition of PPy microstructures via soft template electropolymerization. In this process, hydrogen gas bubbles are formed on the working electrode of 3-electrode electrochemical cell, and upon subsequent application of a positive potential PPy is polymerized around the bubble templates. The resulting hierarchical PPy microstructures on the vat polymerized composite films are shown to increase surface area and consequently improve electroactive response.
Polypyrrole (PPy) is a biocompatible electroactive polymer that incorporates and releases complex molecules via oxidation/reduction reactions utilized as a drug delivery mechanism. However, an increased ion-doping capacity is required to load a clinically sufficient amount of drug into the polymer. In this study, we set out to increase the surface area of PPy films with defined microstructures using a soft-template electropolymerization method. Cyclic voltammetry was used to polymerise PPy films from the aqueous solution of pyrrole and camphorsulfonic acid. By modifying the conditions of this process and changing the setup of electrodes, features of different shapes and sizes were created. PPy films with and without microstructures were subsequently doped with Fluorescein and Rhodamine 6G, model drug substances. Three pH values (2.0, 7.5, 11.0) were chosen as stimuli for drug delivery studies. Drug release was measured using UV-spectroscopy. PPy films modified with microstructures had a higher absorbance peak of fluoresce after release compared to the flat films due to the addition of surface modifications. The pH activated release mechanism was shown to be successful in both flat and microstructured PPy films. Microstructures deposited on the PPy films contributed to the increase in drug incorporation sites, thus providing higher ion-doping capacity. These results show Localized pH changes of the surrounding environment can trigger drug release from the polymer in vivo, where an increase of acidity/alkalinity accompanies pathological processes.
Fabrication of arterial phantoms is enabled through specially developed additive manufacturing techniques in the Organic Mechatronics and Smart Materials Laboratory to produce high resolution 3D conjugated polymer structures. These techniques have been modified to enable fabrication of arterial phantoms through the direct ink writing of polydimethylsiloxane (PDMS) into a microgel support bath. This support bath behaves as a Bingham plastic, deforming under shear stress during extrusion but quickly returning to solid-state, thus supporting the PDMS and allowing the desired structure to be maintained, producing high-resolution complex geometries. Following curing and removal of the PDMS phantom from the support bath, PEDOT:PSS thin films are selectively deposited on the phantom surface. These films have demonstrated significant hygroscopic actuation under an applied electric field. These phantoms may be imaged with Particle image velocimetry (PIV) to characterize the effect of actively changing vessel geometry. PIV can provide the instantaneous full-field velocity profile and is a well-established technique to characterize flow through phantoms fabricated by conventional casting techniques to provide a standard of comparison. To effectively image the device via PIV, the optical properties of the components must be considered. To this end, PDMS and PEDOT:PSS have been employed due to their favourable transmission properties in the visible spectrum. Additionally, PDMS provides a compliant passive structure to be deformed with relatively low force, easing the performance requirements of the actuators. While this device focuses on the actuation of phantom vessel geometry, this technique may be extended to other applications in microfluidics to create onboard peristaltic pumping action and vascular networks.
The intractable nature of the conjugated polymer (CP) polyaniline (PANI) has largely limited PANI-based transducers to monolithic geometries derived from thin-film deposition techniques. To address this limitation, we have previously reported additive manufacturing processes for the direct ink writing of three-dimensional electroactive PANI structures. This technology incorporates a modified delta robot having an integrated polymer paste extrusion system in conjunction with a counter-ion induced thermal doping process to achieve these 3D structures. In this study, we employ an improved embodiment of this methodology for the fabrication of functional PANI devices with increasingly complex geometries and enhanced electroactive functionality. Advances in manufacturing capabilities achieved through the integration of a precision pneumatic fluid dispenser and redesigned high-pressure end-effector enable extrusion of viscous polymer formulations, improving the realizable resolutions of features and deposition layers. The integration of a multi-material dual-extrusion end-effector has further aided the fabrication of these devices, enabling the concurrent assembly of passive and active structures, which reduces the limitations on device geometry. Subsequent characterization of these devices elucidates the relationships between polymer formulation, process parameters, and device design such that electromechanical properties can be tuned according to application requirements. This methodology ultimately leads to the improved manufacturing of electroactive polymer-enabled devices with high-resolution 3D features and enhanced electroactive performance.
This study proposes and demonstrates the design, implementation, and characterization of a 3D-printed smartpolymer sensor array using conductive polyaniline (PANI) structures embedded in a polymeric substrate. The piezoresistive characteristics of PANI were studied to evaluate the efficacy of the manufacturing of an embedded pressure sensor. PANI’s stability throughout loading and unloading cycles together with the response to incremental loading cycles was investigated. It is demonstrated that this specially developed multi-material additive manufacturing process for polyaniline is a good candidate for the manufacture of implant components with smart-polymer sensors embedded for the analysis of joint loads in orthopaedic implants.
The intractable nature of intrinsically conductive polymers (ICP) leads to practical limitations in the fabrication of ICP-based transducers having complex three-dimensional geometries. Conventional ICP device fabrication processes have focused primarily on thin-film deposition techniques; therefore this study explores novel additive manufacturing processes specifically developed for ICP with the ultimate goal of increasing the functionality of ICP sensors and actuators. Herein we employ automated polymer paste extrusion processes for the direct ink writing of 3D conductive polyaniline (PANI) structures. Realization of these structures is enabled through a modified fused filament fabrication delta robot equipped with an integrated polymer paste extruder. This unique robot-controlled additive manufacturing platform is capable of fabricating high-resolution 3D conductive PANI and has been utilized to produce structures with a minimum feature size of 1.5 mm. The required processability of PANI is achieved by means of a counter-ion induced thermal doping method. Using this method, a viscous paste is formulated as the extrudate and a thermo-chemical treatment is applied post extrusion to finalize the complexation.
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